The reaction rate
can be influenced by several factors.
A formula has been derived for reaction rate wherein the most important and most influencing factors are included.
The rate depends on the concentration of the reactants [ ] , on the division/superficion of the substance (homo and heterogeneous), on the temperature (oC or K),
and on the possible presence of a catalyst.
V ≈ [concentration] x division x energy of the particles x catalyst.
In this way, a formula is not very usefull. It is a formula in words. We want numbers and symbols.
You can simplify the formula keeping some circumstances constant during the reaction, in such a way that only the (not constant) concentration do remain in the formula.
Thus we get a mathematical formula:
V = k·[conc.]n
- V: is the rate;
- k: includes the whole of factors kept constant;
- n: is the coefficient of the reactant as in the reaction equation;
- In this way the concentrations of every homogeneous substance appears in the formula. Heterogeneous substances are left out;
- A reactopm where k has a high value, has 'strong' reactants;ntia'
- A reaction where k has a low value, has 'weak' reactants.
Important with reaction rates is the reactivity of particles.
There are particles with a very high reactivity, often called: 'radicals'.
Those radicals are mad - generally spoken - under influence of light and have the peculiar thing that they possess unpaired electron(s).
And radicals are neutral.
Examples: Cl· Br· — C — C — O·
Other attacking particles are those with charges.
Some charged particles like (+, -, δ+ or δ-) show a great reactivity.
We distinguish two possibilities:
An example to explore is the organic reaction between alkonoles and alkanoic acids in the presence of the catalyst sulphuric acid.
- a negative particle attacks a positive particle = nucleophylic mechanism
- a positive particle attacks a negative particle = electrophylic mechanism
propanoic acid + ethanol
ethylpropanoate + water (sulfuric acid = the catalyst)